X-ray imaging apparatuses that convert radiated X-rays into an electric signal (an amount of electric charges) corresponding to the irradiation dose by using an imaging element have been put to practical use. The imaging element includes small X-ray detectors arranged in a two-dimensional matrix. Each of the X-ray detectors includes a stack of a solid-state photodetector element and a scintillator for converting X-rays into visible light. In such X-ray imaging apparatuses, electric charges generated by irradiation with X-rays can be accumulated in a solid-state photoelectric convertor element typically by controlling the voltage applied to the element. Thereafter, the electric charges are read from the element by setting the voltage to be another voltage, and image data based on the accumulated amount of electric charges is generated.
PTL 1 discloses a system that controls an X-ray radiation timing in accordance with an operation state of an X-ray imaging apparatus by allowing an X-ray generation apparatus and the X-ray imaging apparatus to mutually exchange synchronization signals. PTL 2 discloses a technique for detecting an X-ray irradiation timing by detecting a change in current that occurs in an X-ray imaging apparatus when the X-ray imaging apparatus is irradiated with X-rays and for starting imaging in response to the detection.